Light-sensitive diazonium salt materials



Patented Oct. 10,

LIGHT-SENSITIVE DIAZONIUM SALT MATERIALS Paul E. Spoerri, Blue Point,and David P. Habib, Brooklyn, N. Y., assignors to L. L. Ridgway Co., IncNew York, N. Y., a corporation of Texas No Drawing. Application December30, 1947,

Serial No. 794,824

This invention relates to light-sensitive materials, particularly tosuch light-sensitive materials that are of utility in the photographicprinting art, and has for its object the provision of an improvedlight-sensitive material, an improved light-sensitive layer comprisedthereof, and an improved photo-print paper surfaced therewith.

Another object is to provide a light-sensitive diazo-compound widelyutilizable in the photographic printing art and a method of producingsame.

Other objects will be apparent as the invention is more fullyhereinafter disclosed.

In accordance with these objects, we have discovered that certaindiazo-salts of 2:3 dihydroxy naphthalene-B-sulfonic acid arelight-sensitive compounds; that in the presence of alkali or basiccompounds the said salts decompose and undergo internal rearrangement toform a monazo dye of excellent color intensity; and that said salts areof great utility in the forming of light-sensitive layers on the surfaceof suitable materials such as sheet and strip materials heretoforeutilized in the art of photographic printing. More specifically we havefound that these said salts are excellent light-sensitive compounds foruse in the forming of the light-sensitive layer on photo-print paper,all as will hereinafter be more fully disclosed.

Heretofore in the photographic printing art a large number oflight-sensitive diazo-oompounds have been proposed and utilized in theforming of light-sensitive layers on the surface of sheet and stripmaterials such as paper, cloth or photographic film. Inthe normal use ofthese light-sensitive diazo-compounds it is necessary to incorporate inthe light-sensitive layer a proportion of a chemical compound known inthe art as a coupler compound for chemical reaction with thediazo-compound, in the presence of a basic compound, to form the monazodye.

This practice has certain defects and difli- 14 Claims.

diffusing inorganic compounds which detrimentally affect the intensityof the color of the monazo-dye, and otherwise interfere with theobtainance of consistently uniform results. Moreover, it is exceedinglydifficult to obtain in the light-sensitive layer the proper relativeproportions of diazo to coupler compounds to consistently obtain thebest monazo-dye reaction product on treatment with an alkaline compound.

Fhese and other difficulties have led us to discover a light-sensitivecompound which on ex posure to light-radiation of a specific wave lengthor range of wave lengths decomposes into a compound which. isnon-reactive with alkali compounds to form a monazo-dye but which whenunexposed to suchspecific radiation is stable, photo-electrically andchemically, soluble in water or dilute acid solutions, and decomposable,per se, by alkaline compounds to form the desired monazo-dye. We havefound this compound in the 'diazo-salts of 2:3dihydroxynaphthalenefi-sulfonic acid. Various salts of this acid havebeen found suitable for use as a coupler compound for use in associationwith light-sensitive diazo-compounds in the forming of light-sensitivelayers, but its use in this manner has been subject to the same defectsand difliculties hereinabove set forth.

We have discovered that when this sulfonic acid compound is reacted witha light-sensitive diazo-compound, a diam-salt of the sulfonic acid formsand that the light-sensitivity of the basic ion of the diazo-compound issubstantially unaffected by such salt formation. Moreover, whendecomposed by lightradiation the diazosalt compound then becomessubstantially 1m reactive towards mild alkali. The salt compound whenthe basic diazo-ion is not decomposed by culties which it is one of theobjects of this in-g light radiation is readily decomposed by alkalinecompounds with internal rearrangement to form a monazo-dye of maximumintensity. We have further found that light instability of thesediazosalts of this sulfonic acid occurs mostly in the ultra-violet rangeof radiation. materially facilitates the handling and storage This Iproperty tensity, such that variation in color intensity in successiveprints does not occur and desired colors may be obtained through the useof various mixtures of such diazo-salts or of other dye compounds.

As one specific embodiment of the present invention, but not as alimitation thereof, we will disclose the same as it has been adapted tothe production of a diazo-salt of said sulfonic acid which is ofparticular utility in the forming of photo-print paper having alight-sensitive layer comprised of this diazo-salt.

In the art of photo-print paper, particularly direct-print paper, it isespecially desirable to provide a light-sensitive layer which afterexposure to light radiation of a specific wave length or range of wavelengths through a suitable marked or figured positive or negative sheetand treatment with alkali or basic compounds, produces a well-definedsharp outline of the marks or figures on the positive or negative sheetin a dark color of uniform intensity, preferably dark blue or black. Theorganic and inorganic salts of p-diazo-dimethylaniline in mixtureassociation with the sulfonic acid compound above identified haveheretofore been utilized in the forming of light-sensitive layers onsuch photo-print paper in the obtainance of such dark color outlines ofthe marks and figures on the positive sheet. However, such prior art useof a mixture of these two compounds has been subject to the defects anddisadvantages above pointed out.

We have discovered that when an alkaline solution of the sulfonic acidcoupler-compound is added to an acid solution of the diazo-compoundcontaining suflicient free acid to provide an excess of acid over thatrequired to neutralize the free alkali in the alkaline solution of thesulfonic acid compounds said excess providing a weakly acid pH to thecombined solutions, the diazocompound and the sulfonic acid compoundreact to form a sparingly soluble yellow crystalline salt which has thestructural formula (1) indicated below:

This diazo-salt, which may be recovered by filtration and washing withcold water, is decomposed by light radiation in the ultra-violet rangebut only slightlyby radiation in the visible range, withoutdecomposition of the chemical bond between the basic and acidic ionsthereof and when so decomposed is colorless and chemically stabletowards weak alkali. The diazo-salt when treated with an alkalinecompound, such as ammonia vapors (NI-140E), undergoes decomposition andinternal rearrangement in accordance with the following reaction:

The resulting monazo-dye of this reaction is of a deep, intense bluecolor which is highly desirable in the photo-print art. As may be seenfrom the equations and structural formulas given above the diazo-saltand the final dye product does not contain any inorganic groups which inthe presence of free alkali can be converted into color-diffusing orobscuring basic inorganic compounds.

As an example of the formation of this diazosalt, we first form analkaline pH solution containing one molar weight of the sulfonic acidcompound and next form an acid pH solution containing a molar reactingweight of the diazocompound and add the first solution to the secondsolutionrat a slow rate with vigorous stirring to maintain a uniformmixture of the two solutions as the addition of the first solution tothe second solution proceeds. The free acid content of the secondsolution is calculated to be in excess to the free alkali content of thefirst solution by about 10%. The volumes of the two solutions may bewidely varied without essential departure from the invention andpreferably is limited to that calculated to provide for completesolution of all inorganic salts present in the combined solutions andfor a readily filterable filtrate.

The diazo-salt reaction product is sparingly soluble in pure water butthe solubility of the salt increases with increase in the free acidcontent of the solution and with increase in temperature. Initially,therefore, the diazo-salt does not precipitate out of solution but asthe pH of the solution approaches the neutral point, the diazo-salt inexcess of the solubility limit at the temperature of the solutionprecipitates out and we have found that the stirring of the solutionshould continue for an extended time interval after the two solutionshave been mixed for equilibrium conditions to be attained therein. ThepH of the final solution should approximate 6.0 to 6.5 and thetemperature of the solution should be maintained low and at about roomtemperatures for best results. Under these conditions the diazo-saltprecipitates out substantially quantitatively and recoveries of about ofthe theoretical yield are readily obtained. Any excess of the sulfonicacid compound should be avoided. A slight excess of the diazo-compoundover the sulfonic acid compound is preferred. The diazo-salt product ofthis reaction, being crystalline, is relatively easy to separate fromthe filtrate by filtration, preferably on a suction filter with washingwith limited amounts of cold water to remove the filtrate residue beingthe recommended practice.

As typical examples of the two solutions, the first solution consists of15.8 grams of the ammonium or 16 grams of the sodium salt of 2:3-dihydroxynaphthalene-6-sulfonic acid dissolved in millimeters of watercontaining 6 grams of NaOI-I. After making up this solution, the solution should be filtered to remove therefrom any insolubles presenttherein.

The second solution consists of 15 grams of the double zinc chloridesalt of p-diazo-dimethylaniline dissolved in 125 milliliters of watercontaining 1.5 grams of the sodium salt Of naphthalene tri-sulfonic acidand 2 grams of ammonium chloride. This solution after being made up alsoshould be filtered to remove the insolubles and the filtrate should beacidified with 8 grams of sulfuric acid, or enough free acid to p videabout a 10% excessof the free acid over that required to neutralize thefree alkali of the first solution.

The two solutions are mixed together by pouring the first solution intothe second solution slow- 1 with vigorous stirring while maintaining thetemperature of the acid mixture of solutions at a temperatureapproximating room or atmospheric temperatures and after complete mixingthe vigorous stirring is continued for about one-half hour.

As a typical example of a coating solution containing the diazo-saltproduct of the present invention, which is utilizable in the art offorming photo-print paper, th following mixture of in- In the forming ofthis solution the tartaric acid is added to the water and the acidsolution is warmed sufficiently to dissolve the diazosalt producttherein. The glycerine is then added to the acidified diazo-saltsolution; The tartaric acid increases the solubility of the diazosalt inthe water and stabilizes it in solution. The glycerine assists in theretention of the solution on the surface of the photo-print paper. Ifdesired, suitable amounts of a thickener such as gelatin or casein maybe incorporated in the solution to facilitate application of thesolution onto the surface of sheet and strip materials,

such as paper, cloth or photographic (cellulose acetate) film, and thelike.

The application of this solution to the surface of photo-print paper isin accordance with standard practices, and, per se, forms no part of thepresent invention. Following coating the photoprint paper may be storedand handled in accordance with prior art practice with the advantagethat the diazo-salt of the present invention being chemically stable andsubstantially inert except towards alkaline compounds and beingsubstantially insensitive to light radiation above the ultra-violet waveband, is much easier to store and handle and remains radiationsensitivetowards ultra-violet radiation longer than prior art photo-print paperusually does.

After exposure of the coated sheet to ultraviolet radiation in the usualmanner through a transparent positive or negative sheet the yellow colorof the sheet in the area subjected to ultraviolet radiation isde-colorized leaving a picture in yellow representative of the pictureon the transparent positive or negative sheet through which theradiation is passed. On subjecting the photo-print paper to moistammonia (NHrOI-I) vapors the yellow figure changes to a dark, intenseblue color by decomposition and internal rearrangement of the diazo-saltinto a monazodye in accordance with the equation given above.

The advantages of the diazo-salt product of the present invention overprevious lightsensitive diazo-compounds are believed to be apparent tothose skilled in the art from the above disclosure. However, it isbelieved most important to point out that the preservation of the l to 1ratio of diazo-compound to coupler compound in the diazo-salt product inthose areas not decomposed by the light radiation insures a color ofconstant and consistent intensity in the monazo-dye product formed byalkali decomposition. Further, decomposition of the basic ,diazo-ion'bylight radiation inactivates the diazo-salt for alkaline reaction to forma monazo-dye, thus maintaining the 1 to 1 ratio of diazo to coupler ionsin the undecomposed areas. Finally, the absence of inorganic groups inthe diazo-salt of the present invention, particularly those containingbasic metallic ions forming insoluble hydroxides or oxy-compounds in thepresence of alkaline compounds, eliminates the possibility of colordiffusion due to these reaction products.

In addition by its process of manufacture and precipitation from acid pHsolution the diazosalt is substantially free of associated organiccompounds and tarry residues.

In place of the p-diazo-dimethylaniline compound, above given, any otherwater or acid soluble salt of this diazo-compound may be employed in themanufacture of the diazo-salt of the present invention. Various otherlight-sensitive diazo-compounds also may be substituted for thep-diazo-dimethylaniline compound in the manufacture of light-sensitivediazo-salts of this sulfonic acid compound without essential depar turefrom the invention, where monazo-dyes of different colors are desired.In substitution for the sulfonic acid compound above identified,varifunctioning as a coupler compound with diazocompounds may besubstituted without essential departure from the invention, where colorvariations in the monazo dye product of alkaline reaction with thediaZo-salt, are desired.

In association with the diazo-salt of the present invention, we employ,also, an amount of a permanent yellow dye which is suificient to imparta substantially black color to the monazo-dye product formed by reactionof the diazo-salt with an alkaline compound. In general, this amount ofyellow dye approximates 30%.

Various modifications of and departures from the invention will occur tothose skilled in the art and all those are contemplated by us as mayfall within the scope of the following claims.

What we claim is:

1. A light-sensitive compound consisting of a diaZo-salt of 2:3dihydroxynaphthalene-G-sulfonic acid.

2. A light-sensitive compound consisting of the p-diazo-dimethylanilinesalt of 2:3, dihydroxynaphthalene-G-sulfonic acid.

3. A light-sensitive layer comprised of a dia zosalt of 2:3dihydroxynaphthalene-fi sulfonic acid.

4. A light-sensitive layer comprised of the pdiazo-dimethylaniline saltof 2:3 dihydroxynaphthalene-G-sulfonic acid.

5. Photo-print paper having a light-sensitive layer on the surfacethereof comprised of a diazosalt of 2:3 dihydroxynaphthalene-6-sulfonicacid.

6. .Photo-print paper having a light-sensitive layer on the surfacethereof comprised of the pdiazo-dimethylaniline salt of 2:3dihydroxynaphthalene-B-sulfonic acid.

7. A coating composition for forming lightsensitive layers on thesurface of sheet and strip materials, said composition consisting of aweakly acid aqeous solution of a light-sensitive diazosalt of 2:3dihydroxynaphthalene-6-sulfonic acid.

8. The coating composition of claim '7, said solight-sensitive saltbeing the p-diazo-dimethylaniline salt of said sulfonic acid.

11. Photo-print paper having a light-sensitive layer comprised of thecoating composition of claim 7. I

12. The method of forming a diazo-salt of 2:3dihydroxynaphthalene-S-sulfonic acid which comprises adding an alkalinepH solution of the sulionic acid compound to an acid pH solution of adiaZo-compound slowly and with vigorous stirring and while maintainingan acid pH in the mixture of solutions and continuing the stirring ofthe acid pH mixture of the solutions for an extended time interval Whilethe temperature of the solution cools to atmospheric temperatures andequilibrium conditions are attained therein and separating theprecipitated salt product from the solution.

13. The method of forming the p-diazo-dimethylaniline salt of 2:3dihydroxynaphthalenefi-sulfonic acid which comprises forming an alkalinepI-I solution of the sulfonic acid compound and an acid pH solution ofthe diazo-compound, said acid solution containing an excess of free acidover that required to neutralize the free alkali content of the alkalinesolution, mixing the alkaline pH solution with the acid pH solution at aslow rate and with vigorous agitation sufiicient to maintain a uniformdispersion of the alkaline pH solution in the acid pH solution,continuing the agitation of the solution for an extended time intervalafter the alkaline pH solution has been all added to the acid pHsolution to permit the mixture of solutions to cool down to roomtemperatures and to attain equilibrium conditions therein, andseparating therefrom the precipitated salt product obtained thereby.

14. The method of claim 13, wherein the two said solutions contain molarreacting weights of the sulfonic acid compound and diazo-compound,respectively, and the volumes of the two solutions are at leastsuflicient to hold in solution on admixture substantiall all solublereaction products except the precipitated salt product.

. PAUL E. SPOERRI.

DAVID P. HABIB.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS OTHER REFERENCES K. H. Saunders, The AromaticDiazo Compounds and Their Technical Application, pp. 164 171 (1936). V 1

1. A LIGHT-SENSITIVE COMPOUND CONSISTING OF A DIAZO-SALT OF 2:3DIHYDROXYNAPHTHALENE-6-SULFONIC ACID.
 6. PHOTO-PRINT PAPER HAVING ALIGHT-SENSITIVE LAYER ON THE SURFACE THEREOF COMPRISED OF THEPDIAZO-DIMETHYLANILINE SALT OF 2:3 DIHYDROXYNAPHTHALENE-6-SULFONIC ACID.